证:j(m)=IDFS[X1(k)·x2(k) N ∑x(k)X2(k)W k=0 N2D2, (m)Wo JX2(k)WN ∑x(m)∑X2(k)Wmm 1-m1 2 y(n)  IDFS[X (k) X (k)]   证：  1 1 2 0 1 ( ) ( ) N kn N k X k X k W N        1 1 1 2 0 0 1 [ ( ) ] ( ) N N mk kn N N k m x m W X k W N           1 1 ( ) 1 2 0 0 1 ( )[ ( ) ] N N n m k N m k x m X k W N            1 1 2 0 ( ) ( ) N m x m x n m       